The present invention relates to a stepping apparatus capable of large angle oscillation and, in particular, to an angular stepping apparatus particularly suitable for automatic tool changing wherein an output shaft secured on a roller wheel plate is allowed to oscillate for large angles by a pair of parallel plate cams in combination with a plurality of rollers provided on the wheel plate.
Automatic processing machineries enable automatic changing of tools between a main spindle and a tool magazine by using an apparatus known as the automatic tool changer (ATC). As shown in FIGS. 1A through 1F, the operation of the ATC mainly comprises the sequential movements of tool-grasping, tool-drawing, tool-changing, tool-loading, returning to position and coming into standby.
FIGS. 1A-1F are schematic views showing the sequential movements during operation of the ATC. In the illustrated ATC, an output shaft O is secured at one end thereof with a swing arm L having tool holding claws A and B which mate, respectively, with the tools on the main spindle S and the tool magazine M to perform the tool changing operation.
FIG. 1A is a schematic view showing the swing arm L in a standby position. When starting the automatic tool changing operation, the output shaft O rotates the swing arm L from its initial stationary condition to perform the tool-grasping operation, bringing it from the "standby" position into a "tool drawing" position as shown in FIG. 1B, and causing the tool holding claws A and B to grasp the tools on the main spindle S and the tool magazine M to perform the "tool-grasping operation".
FIG. 1B is a schematic view showing the swing arm L in the "tool-drawing" position. After the tool holding claws A and B caught the tools on the main spindle S and the tool magazine M, respectively, the output shaft O moves axially outwardly to remove the tools, respectively, from the main spindle S and the tool magazine M, thereby to accomplish a "tool drawing" operation.
FIG. 1C is a schematic view showing the "tool-changing" operation. After the tools on the main spindle S and the tool magazine M are withdrawn, the swing arm L rotates 180 degrees such that the tool claws A and B each change its place with the other, causing the tool removed from the tool magazine M to be changed with the tool on the main spindle S.
FIG. 1D is a schematic view showing the "tool-loading" operation. At this point, the output shaft O is moved axially inwardly after the "tool-changing" operation such that the tools in the claws B and A are loaded on the main spindle S and the tool magazine M, respectively.
FIG. 1E is a schematic view showing that the swing arm L is ready to perform the "returning to position" operation. After the tools are loaded, respectively, on the main spindle S and the tool magazine M by the swing arm L, the arm L rotates an angle, and returns to its "standby" position (as shown in FIG. 1F), thus being ready for the next cycle of the automatic tool changing operations.
Instead of the earlier time-consuming tool changing operations by the hydraulic driving system, conventional ATC's recently tend to use a so-called "roller gear cam" to perform the oscillating and indexing of the swing arm in the tool changing operations, and to perform the axially upward and downward movements of the swing arm in the tool changing operations by using a grooved cam in association with link means. For example, Japanese New Utility Model Laid-Open Sho 63-113530 discloses an ATC employing a roller gear cam and plate cams. While such a changer achieves the operations and the purpose of the automatic tool changers, the roller gear cams as employed are cams of the three-dimensional type which are expensive to manufacture and not easy to have the required tolerance. In addition, the oscillating movements of the link driven by the grooved cam results in non-positive driving therebetween, thus causing loss of the benefits of the positive driving by using the roller gear cams.
In conventional parallel indexing cam structure, for example, the "Indexing Cam Structure" disclosed in U.S. Pat. No. 2,986,949 issued to Edward W. Lancaster, et al, Jun. 6, 1961, although stepping indexed positioning operation can be achieved by using a pair of parallel or juxtaposed plate cams driving a roller wheel plate (i.e., a wheel plate alternatively and pivotally provided on both sides with a number of rollers), said indexing cam structure enables its output shaft (i.e., the shaft of the roller wheel plate) to step forward in time-sequence only in one direction of rotation but the output shaft is incapable of effecting reverse rotational movement, thus impossible for the output shaft to effect an oscillating movement. As a result, said parallel indexing cam structure can not provide the movements for the tool grasping and returning to position operations, and thus is unstable for the automatic tool changers.
U.S. Pat. No. 4,416,165 issued to Kramer, et al, Nov. 22, 1983, discloses a "Stepping Gear" in which a pair of coaxially juxtaposed plate cams are used for driving a roller wheel plate having a number of rollers. Said stepping gear, being a parallel indexing cams structure, provides accurate indexed forward movement and the output shaft of the roller wheel plate is capable of reverse movement by having undercut in one of the cams. However, said stepping gear is basically an indexing mechanism providing very small oscillating angles in reverse movement such that it is suitable only for packaging operations by the packaging machines. Said stepping gear for maintaining positive driving between the cams and the rollers does not provide the oscillating angles required for the "tool grasping" and "returning to position" operations in a automatic tool changer. In particular, some recently developed automatic tool changers require oscillating angles of more than 45 degrees for automatic tool changing operations. Said conventional stepping gears are thus becoming even more unsuitable for use in the automatic tool changers.
U.S. Pat. No. 4,833,772 issued to Mitsuo Kobayashi, et al, May 30, 1989, discloses an "Automatic Tool Changing Apparatus" in which a cam index mechanism for rotating a swing arm by using a pair of juxtaposed plate cams driving a roller wheel plate is in fact an application of the stepping gear disclosed in the aforementioned U.S. Pat. No. 4,416,165. Said mechanism is basically a conventional parallel indexing cam structure and provides only an indexed positioning function. Said mechanism is basically a conventional parallel indexing cam structure and provides only an indexed positioning function such that it is impossible for its output shaft to oscillate in reverse movement but to provide a forward stepping rotation.